Vine crop, e.g. tomato harvesters for the infield recovery of tomatoes by separating them from the vines are presently widely used. Such a harvester is described, for example, in U.S. Pat. No. 3,437,151.
Briefly, automatic tomato harvesters are large, normally self-propelled machines which move along rows of tomato plants in the field. A knife severs the tomato vines from the roots and the vines together with attached tomatoes are then picked up by a rearwardly and upwardly inclined elevator which transports the vines and the tomatoes to a tomato processing apparatus, normally a shaker. In the shaker the vines are subjected to vibrations to loosen the tomatoes from the vines. The tomatoes are collected while the vines are discharged to the ground and later plowed under.
The severing of the vines from the root stock and the initial pick-up of the vines by the elevator are critical operations. For an efficient operation, it is necessary to pick up substantially all tomatoes and further to minimize the pick up of dirt and debris. This requires that the lowermost or leading edge of the elevator be positioned closely adjacent the ground at a constant spacing with respect thereto. Since the wheels on which the harvester moves through the field ride in furrows between the tomato rows relative irregularities between the furrows and the row surfaces as well as ground surface irregularities in the rows can cause variations in the distance between the leading edge of the elevator and the ground. Thus, the leading edge moves too close to the ground so that it contacts the soil and picks up undesirable dirt. Alternatively, the leading edge may be raised too high so that not all of the tomatoes are collected.
To alleviate this problem, it has been suggested to provide control mechanism which maintains the spacing between the ground surface and the leading edge of the elevator relatively constant. Generally speaking, such mechanisms included a sensor wheel or shoe mounted to the elevator adjacent to but aft of the leading edge. The intent of such sensors was to raise or lower the leading edge in response to relative vertical movements of the harvester or in response to surface irregularities such as mounds of soil or soil depressions. Such sensors are disclosed, for example, in U.S. Pat. Nos. 3,550,362; 3,643,407; 3,851,451; and 3,704,574.
A shortcoming of these sensors is their positioning relative to the leading edge. Since the sensors are disposed aft of the leading edge, the latter arrives at a surface irregularity ahead of the sensor. Consequently, the sensor cannot timely adjust the relative vertical position of the leading edge so that the edge, at least for a while, is either too high or too low, leading to the above-discussed drawbacks.
In addition, in instances in which sensor wheels were employed, the wheels were fitted with radial arms the free ends of which were permitted to ride over the ground and sense the distance between the header and the ground surface. It is apparent that as the wheel rolls over the ground the radially oriented tines had a tendency to spear and thus damage soft fruit such as tomatoes. Tomatoes damaged in this manner became, of course, unusable and had to be discarded. Moreover, the tines further tended to spear and pick up vines which could become entangled in the sensor wheel and render it inoperative. This, in turn, required that the harvester be stopped and the sensor wheel be cleaned which entailed costly harvester downtimes and was, therefore, economically undesirable.
It is believed that the above-discussed short-comings of prior art sensors were at least in part responsible for the rather common absence of automatic elevator adjustment mechanisms on harvesters used in the field. Instead, the operator of the harvester had the responsibility of manually controlling the relative height of the leading elevator edge. This commanded his constant attention, leaving him correspondingly less time to attend to the other functions of the machine which could in turn adversely affect the harvesting operation.